The present invention relates to an arrangement for connecting a low-pressure inlet of a gas analyzer with a test gas connection operated at a higher pressure level, comprising a connection line with a connection for the low-pressure connection as well as a connection for the test gas connection, another gas flow connection leading into the connection line, a valve body which operates in the connection line and controls its gas flow cross-section for the connection to the low-pressure connection, to a mass spectrometer having such an arrangement and to a use of the above-mentioned arrangement and of the mass spectrometer.
As a typical example of the mentioned gas analyzers, mass spectrometers are frequently used, for example, for analyzing gas compositions. Particularly in the case of vacuum treatment processes, such as PVD, PECVD or CVD processes, it is increasingly necessary to precisely control the treatment gas atmosphere particularly for control the treatment gas atmosphere particularly for critical applications. In this case, CVD processes are also used under atmospheric pressure conditions.
The gas analyzers normally operate in vacuum ranges which are much lower, for example, in the 10.sup.-3 bar range, than the process pressures of, for example, 0.1 mbar to 100 mbar, which are used in the above-mentioned processes. The resulting problems during the coupling of the gas analyzers of the above-mentioned type to the test gas atmospheres to be analyzed are known: Falsification of the gas composition when transferring the gas to the analyzer, falsification of the gas composition in the analyzer itself or damage to or at least contamination of the analyzer by the gas to be tested.
This problem becomes worse when the test gas is a reactive gas which may react with solid phases in the connection system and/or at the analyzer, or when such a reactive gas forms solid reaction products which are deposited in the above-mentioned connection system and/or on the input side of the gas analyzer.
Different approaches are known for solving these problems.
For example, a first known approach consists of providing a pressure stage in the form of a screen in the connection line. The providing of such a fixed pressure stage, as known, for example, from U.S. Pat. No. 5,318,752, has the disadvantage that it often cannot utilize the highest possible operating pressure of the gas analyzer. In the case of changing pressures of the gas to be analyzed, a variation possibility of the screen or the pressure stage would therefore be desirable. only in this manner, an optimal relationship can be established in every case between the useful signal and the background signal at the analyzer.
This is ensured by the also known provision of an adjustable leakage valve as the pressure stage. However, the providing of a valve mechanism in the above-mentioned connection system results in serious disadvantages with respect to the enlargement of he gas-absorbing surfaces, the introducing of additional dead volumes with corresponding memory effects, as well as with respect to the contamination of the gas atmosphere, for example, by mechanical abrasion.
The disadvantages of the above-mentioned mechanical leakage valves were eliminated partially by the introduction of the so-called "virtual valves" but without completely retaining the advantages of the mechanical valves. The "virtual valves" are gas-dynamic pressure stages or ends, in the case of which the analysis gas flow to toward the analyzer encounters a barrier gas flow in the counterflow. In the case of a corresponding barrier gas flow, the analysis gas can largely be kept away from the test inlet of the analyzer. In this respect, reference is also made to the above-mentioned U.S. Pat. No. 5,318,752.
The most important disadvantage of the "virtual valves" is the fact that the barrier gas flow does not permit the implementation of a complete locking, as required, for example, when ventilating a process chamber to which the analyzer is connected. In addition, a point is formed at the mouth of the gas inlet for the barrier gas into the connection system at which memory effects may occur. This may take place in that, for example, old gas residues remain adsorbed at the above-mentioned gas inlet, which gas residues later, when the barrier gas is switched off, are desorbed and will falsify analyses which follow.
U.S. Pat. No. 3,633,027 discloses a so-called Becker-Ryhage-Separator on which a pump connection is led by way of an inlet nozzle to the inlet of a gas-phase chromatograph. Opposite an inlet nozzle to the gas-phase chromatograph, an outlet nozzle is provided to a second--a mass spectrometer--stage. A slide, which can be adjusted into two discrete positions, is guided in a guide housing and closes or opens the above-mentioned nozzles.
DE-OS 29 39 893 shows a mass spectrometer acted upon by way of a connection line by two connections, which connection line has a third connection for the mass spectrometer. A valve body operated in the pulse operation in this case controls the flow cross-section from the connection line to the mass spectrometer.